Android NDK开发图片处理(五)

做过Java的同学可能经常会遇到一些关于图片处理的

例如类似QQ离线头像显示灰的。最快的算法是用colorMatrix来实现。这里通过Java调用JNI来处理每一个像素来实现。

对每一个像素点取出RGB每个通道的值R,G,B
cololr=(R+G+B)/3;这个值是需要修改的值
将原来GRB的通道全设置成color的值

首先先看用Java怎么实现这个功能

 public Bitmap convertGrayImg(int resID)

    {

        Bitmap img1=((BitmapDrawable) getResources().getDrawable(resID)).getBitmap();

        int w=img1.getWidth(),h=img1.getHeight();

        int[] pix = new int[w * h];

        img1.getPixels(pix, 0, w, 0, 0, w, h);

        int alpha=0xFF<<24;

        for (int i = 0; i < h; i++) {

            for (int j = 0; j < w; j++) {

                // 获得像素的颜色

                int color = pix[w * i + j];

                int red = ((color & 0x00FF0000) >> 16);

                int green = ((color & 0x0000FF00) >> 8);

                int blue = color & 0x000000FF;

                color = (red + green + blue)/3;

                color = alpha | (color << 16) | (color << 8) | color;

                pix[w * i + j] = color;

            }

        }

        Bitmap result=Bitmap.createBitmap(w, h, Config.RGB_565);

        result.setPixels(pix, 0, w, 0, 0,w, h);

        return result;

    }

下面是JNI来处理

c++代码如下

#include <jni.h>

#include <string>

extern "C"{

jintArray JNICALL

        Java_com_tmf_test_ndk_bitmap_MainActivity_getImgToGray(JNIEnv *env, jobject instance,

                                                               jintArray data_, jint w, jint h);

}

JNIEXPORT jintArray JNICALL

Java_com_tmf_test_ndk_bitmap_MainActivity_getImgToGray(JNIEnv *env, jobject instance,

                                                       jintArray data_, jint w, jint h) {

    jint *data;

    data = env->GetIntArrayElements(data_, NULL);

    if (data == NULL) {

        return ; /* exception occurred */

    }

    int alpha = 0xFF << ;

    for (int i = ; i < h; i++) {

        for (int j = ; j < w; j++) {

            // 获得像素的颜色

            int color = data[w * i + j];

            int red = ((color & 0x00FF0000) >> );

            int green = ((color & 0x0000FF00) >> );

            int blue = color & 0x000000FF;

            color = (red + green + blue) / ;

            color = alpha | (color << ) | (color << ) | color;

            data[w * i + j] = color;

        }

    }

    int size=w * h;

    jintArray result = env->NewIntArray(size);

    env->SetIntArrayRegion(result, , size, data);

    env->ReleaseIntArrayElements(data_, data, );

    return result;

}

activity实现如下

package com.tmf.test.ndk.bitmap;

import android.graphics.Bitmap;

import android.graphics.drawable.BitmapDrawable;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.widget.ImageView;

import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    // Used to load the 'native-lib' library on application startup.

    static {

        System.loadLibrary("native-lib");

    }

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        // Example of a call to a native method

        ImageView tv = (ImageView) findViewById(R.id.image);

        tv.setImageBitmap(getJniBitmap());

    }

    public Bitmap  getJniBitmap(){

        Bitmap bitmap=((BitmapDrawable) getResources().getDrawable(R.mipmap.timg)).getBitmap();

        int w=bitmap.getWidth(),h=bitmap.getHeight();

        int[] pix = new int[w * h];

        bitmap.getPixels(pix, 0, w, 0, 0, w, h);

        //通过ImgToGray.so把彩色像素转为灰度像素

        int[] resultInt=getImgToGray(pix, w, h);

        Bitmap resultImg=Bitmap.createBitmap(w, h, Bitmap.Config.RGB_565);

        resultImg.setPixels(resultInt, 0, w, 0, 0,w, h);

        return resultImg;

    }

    public native int[] getImgToGray(int[] data,int w,int h);

    private int[] bitmapToArray(int resID)

    {

        Bitmap bitmap=((BitmapDrawable) getResources().getDrawable(resID)).getBitmap();

        int w=bitmap.getWidth(),h=bitmap.getHeight();

        int[] pix = new int[w * h];

        bitmap.getPixels(pix, 0, w, 0, 0, w, h);

      return pix;

    }

}

效果如下

bitmap.h

目录android-ndk-r10e\platforms\android-21\arch-arm\usr\include\android里面

bitmap.h头文件中的内容并不多，主要有这些部分组成：

结果状态定义。
位图格式枚举。
位图信息结构体。
位图操作函数声明。

define ANDROID_BITMAP_RESULT_SUCCESS

#define ANDROID_BITMAP_RESULT_BAD_PARAMETER     -1

#define ANDROID_BITMAP_RESULT_JNI_EXCEPTION     -2

#define ANDROID_BITMAP_RESULT_ALLOCATION_FAILED -3

/* Backward compatibility: this macro used to be misspelled. */

#define ANDROID_BITMAP_RESUT_SUCCESS ANDROID_BITMAP_RESULT_SUCCESS

这里定义了对Bitmap进行操作时的结果，分别对应成功，错误的参数，JNI异常，内存分配错误，至于最后一个，这是个梗。Google工程师在定义NDK的时候写错一个单词，居然没有检查就发布了，然后就233333333了。看来IDE的拼写检查对自己人也有好处。

位图格式枚举

enum AndroidBitmapFormat {

    ANDROID_BITMAP_FORMAT_NONE      = ,

    ANDROID_BITMAP_FORMAT_RGBA_8888 = ,

    ANDROID_BITMAP_FORMAT_RGB_565   = ,

    ANDROID_BITMAP_FORMAT_RGBA_4444 = ,

    ANDROID_BITMAP_FORMAT_A_8       = ,

};

一般而言，常见的位图格式有RGB_565 、RGBA_8888、 ARGB_8888、 RGBA_4444、 ARGB_4444、 ALPHA_8

位图信息结构体

typedef struct {

    uint32_t    width;

    uint32_t    height;

    uint32_t    stride;

    int32_t     format;

    uint32_t    flags;      // 0 for now

} AndroidBitmapInfo;

width表示图片的宽度(列数)，height表示图片的高度(行数)，stride为行跨度，具体含义后面会进行介绍。最后一个参数已经被弃用，其值始终为0。

位图操作函数声明

int AndroidBitmap_getInfo(JNIEnv* env, jobject jbitmap,

                          AndroidBitmapInfo* info);

int AndroidBitmap_lockPixels(JNIEnv* env, jobject jbitmap, void** addrPtr);

int AndroidBitmap_unlockPixels(JNIEnv* env, jobject jbitmap);

AndroidBitmap_getInfo：获取当前位图信息。
AndroidBitmap_lockPixels：锁定当前位图像素，在锁定期间该Bitmap对象不会被回收，使用完成之后必须调用AndroidBitmap_unlockPixels函数来解除对像素的锁定。
AndroidBitmap_unlockPixels：解除像素锁定。

JNIEXPORT jboolean JNICALL

Java_com_tmf_test_ndk_bitmap_MainActivity_getImgToGray1(JNIEnv *env, jclass type, jobject jsrcBitmap,

                                                        jobject desBitmap) {

    AndroidBitmapInfo srcInfo, dstInfo;

    if (ANDROID_BITMAP_RESULT_SUCCESS != AndroidBitmap_getInfo(env, jsrcBitmap, &srcInfo)

        || ANDROID_BITMAP_RESULT_SUCCESS != AndroidBitmap_getInfo(env, desBitmap, &dstInfo)) {

        LOGE("get bitmap info failed");

        return false;

    }

    void *srcBuf, *dstBuf;

    if (ANDROID_BITMAP_RESULT_SUCCESS != AndroidBitmap_lockPixels(env, jsrcBitmap, &srcBuf)) {

        LOGE("lock src bitmap failed");

        return false;

    }

    if (ANDROID_BITMAP_RESULT_SUCCESS != AndroidBitmap_lockPixels(env, desBitmap, &dstBuf)) {

        LOGE("lock dst bitmap failed");

        return false;

    }

    int w = srcInfo.width;

    int h = srcInfo.height;

    int32_t *srcPixs = (int32_t *) srcBuf;

    int32_t *desPixs = (int32_t *) dstBuf;

    int alpha = 0xFF << 24;

    for (int i = 0; i < h; i++) {

        for (int j = 0; j < w; j++) {

            // 获得像素的颜色

            int color = srcPixs[w * i + j];

            int red = ((color & 0x00FF0000) >> 16);

            int green = ((color & 0x0000FF00) >> 8);

            int blue = color & 0x000000FF;

            color = (red + green + blue) / 3;

            color = alpha | (color << 16) | (color << 8) | color;

            desPixs[w * i + j] = color;

        }

    }

    AndroidBitmap_unlockPixels(env, jsrcBitmap);

    AndroidBitmap_unlockPixels(env, desBitmap);

    return true;

}

Java层代码

public  native boolean getImgToGray1(Bitmap src,Bitmap des);

效果和上面都一样的，只是这个直接在底层处理bitmap对象

如果有以下异常

  E:\test\NdkBitmap\app\src\main\cpp/native-lib.cpp:52: undefined reference to `AndroidBitmap_getInfo'

  E:\test\NdkBitmap\app\src\main\cpp/native-lib.cpp:53: undefined reference to `AndroidBitmap_getInfo'

  E:\test\NdkBitmap\app\src\main\cpp/native-lib.cpp:59: undefined reference to `AndroidBitmap_lockPixels'

  E:\test\NdkBitmap\app\src\main\cpp/native-lib.cpp:64: undefined reference to `AndroidBitmap_lockPixels'

  E:\test\NdkBitmap\app\src\main\cpp/native-lib.cpp:86: undefined reference to `AndroidBitmap_unlockPixels'

  E:\test\NdkBitmap\app\src\main\cpp/native-lib.cpp:87: undefined reference to `AndroidBitmap_unlockPixels'

我用的是Android studio自带的cmake打包的，需要在

在CMakeLists.txt 添加 -ljnigraphics

target_link_libraries( # Specifies the target library.

                       native-lib

                       -ljnigraphics

                       # Links the target library to the log library

                       # included in the NDK.

                       ${log-lib} )